I'm not really an expert on this topic. We're an IMS shop, but all the
IMS topics
are hidden behind a site specific application framework, so that most of
IMS is
not visible to the applications. In my earlier life, I worked at a
company, which used
CICS on VSE. So my impression is:
- CICS is faster, easier to handle, all transactions in one address
space, has lots
of features like transient data queues and temp store queues that are
maybe missing
in IMS, but
- CICS programs need to be reentrant, no static storage allowed -
because different
transactions used in the same address space share the same copy of the
load module.
This may be no problem any more with modern LE compilers and WSA
(writable static
and RENT option, although for example with PL/1 IBM recommends not to
use it. We
don't use it and tell our developers to make the modules "naturally"
reentrant - although
IMS doesn't require it)
- IMS doesn't require the modules to be reentrant, because every
transaction has it's
own region.
- even VSAM files for examples are opened by CICS (once per address space)
and are used not by normal file operations (OPEN FILE(x) in PL/1, for
example),
but through EXEC CICS commands. This is different for IMS, AFAIK -
normal file
operations there.
- as a consequence: one misbehaving module in CICS can crash the whole
CICS address space (at least I think so). With IMS, individual regions
can be recovered
and restarted.
But I may be wrong on some details.
Kind regards
Bernd
Am 16.02.2012 19:56, schrieb Ian Steyn:
Frank,
IMS DC does the same thing as CICS, but completely different.
An IMS control region with its message region function basically like CICSPlex
with AOR's and TOR's.
Transactions in IMS can be tied to specific message regions and you can have
several message regions tied to a control region. Transactions can be balanced
across the message regions, and on misbehaving message region will not affect
any of the other message regions in the same control region.
IMS was designed from the start to process transaction this way whereas CICS
was build to handle all transaction in one region. The TOR, AOR concept was
added on to CICS afterwards.
IMS is a beast to administer and is, in my opinion, less flexible than CICS.
CICS is very easy to maintain. IE: "CEDA DEFINE PROG(XXX_" compared to running
gens etc. but one bad behaving transaction can bring everything to a halt in CICS.
Ian
http://www.cicsworld.com
----------------------------------------------------------------------
For IBM-MAIN subscribe / signoff / archive access instructions,
send email to lists...@bama.ua.edu with the message: INFO IBM-MAIN
----------------------------------------------------------------------
For IBM-MAIN subscribe / signoff / archive access instructions,
send email to lists...@bama.ua.edu with the message: INFO IBM-MAIN
